1. Field of the Invention
The invention relates to vascular stents and, more particularly, comprises a vascular stent which facilitates cellular transplant in animal bodies such as humans.
2. Background Information
Stents are commonly used to support blood vessels whose walls have been damaged or to bridge and repair vessels that have been injured. Typically, such stents consist of an expansible mesh which is collapsible during insertion into a vessel and thereafter expansible (e.g., by means of a balloon catheter) to firmly engage the inner wall surface of a blood vessel and secure it in place.
In addition to providing structural support, some stents have often been coated with various medications for such purposes as minimizing inflammation and providing treatment. Examples of commonly used stents are described in “Handbook of Coronary Stents”, 2d ed., by Patrick W. Serruys and Michael J B Kutryk, Eds. (1997, 1998). In addition, some stents have been coated with vascular endothelial cells in order to promote endothelialization and thereby lessen clotting and decrease resteonsis.
It has been known to introduce living, functional animal cells into human bodies in order to remedy deficiencies in the production of necessary hormones and other body products. Usually, the cells are introduced by surgically implanting them in the peritoneal cavity, or by injecting them into the portal vein where they lodge in the liver. In the peritoneal cavity, blood vessels must grow and develop to nourish the cells and transport their therapeutic products (e.g., insulin) to the sites where they will be used. In the liver, the sinusoids provide blood, but the cells may obstruct these sinusoids, thus inducing portal hypertension and even cirrhosis of the liver. Other sites have been tried (e.g., the renal capsule); however, the lack of immediate vascular access poses problems for these approaches.
Auto transplantation of parathyroid glands that have been removed because of extensive thyroid surgery have been performed in the forearm with variable results, as has autotransplantation by way of pancreatectomy for neoplasm, where the islet cells producing insulin and/or glucagon may be preserved for autotransplantation to prevent diabetes. Other examples of autotransplantation include the use of the patients' stem cells to repair injured organs or tissue.
Microporous or semipermeable membranes have been used in connection with transplants; examples are described in U.S. Pat. Nos. 4,209,776, 5,911,704, and 5,704,910. A disadvantage to such an approach is that the pores of these membranous devices can be plugged with proteinaceous deposits. Further, the membranes also tend to increase clotting. In each case this compromises the viability of the transplanted cells and their ability to function. Also, vascular grafts or combination stent-grafts using Dacron or ePTFE increase thrombogenicity and compromise blood flow by increasing the inflammatory response with neointimal proliferation.
Stents have also been combined with heart valves, to anchor them in place. Some of these heart valves contain living cells.